“When Jon Marden and Ana Elizabeth decided to split in 2005 after 13 years of marriage, they both moved out of the house they shared in the woods near Santa Cruz, Calif. Their three children, however, stayed put. When it was Elizabeth’s turn to look after the kids, she stayed with them. When it was their father’s turn, she left and he took over.

This arrangement, sometimes known as nesting, has emerged over the past decade as an offshoot of the equal-custody, or co-parenting, trend. It requires what would seem to many splitting couples to be a mind-bogglingly amicable relationship and, usually, a robust pot of marital funds, since the number of homes expands from one to three: his, hers and the children’s.”